This application claims the priority of German patent document 198 28 804.2, filed Jun. 27, 1998, the disclosure of which is expressly incorporated by reference herein.
The invention relates to a process for simulating echo signals for Doppler radar systems.
To check and test Doppler radar systems, radar simulators are frequently used that receive a radar signal of the Doppler radar system to be tested, subject it to the action of a Doppler shift, and then transmit it back again to the radar system.
These simulators usually work according to the following principle illustrated in FIG. 1. The transmitting signal of the Doppler radar system is received by the simulator antenna An and converted to an intermediate frequency (ZF) in the mixer Mi. The reference letters LO stand for the local oscillator that is used to convert into the intermediate frequency. On the ZF plane this signal is subjected to the action of a Doppler frequency in a modulator Mo connected to a transmit/receive isolating circulator CR. The modulator can be constructed as a single mixer in order to generate a double sideband Doppler signal, or it is conceived as a single sideband (ESB) modulator for generating a single sideband Doppler signal. Following the modulation this signal is delayed, if necessary, before it is then converted up again to the radar frequency (HF). The signal that is modulated thus is beamed back over the simulator antenna An to the radar system and can be processed as an echo signal. Such a simulator is described, for example, in xe2x80x9cSimulation of Radar Targetsxe2x80x9d, by G. Plasberg, Frequency 45 (1991), pp. 5-6.
U.S. Pat. No. 3,329,953 discloses another process of this class, where the echo signals are simulated by means of a bidirectional phase shifter, which is connected in series to a circulator. The other outputs of the circulator are either terminated by short circuits or connected together by means of an amplifier in order to increase the simulated signal.
The object of the present invention is to provide a process for simulating echo signals for Doppler radar systems that can be realized inexpensively.
The front ends of many Doppler radar systems have single switches, which can be used, for example, to switch over from the transmitting to the receiving branch or which are necessary for activating different antennas. For example, radar systems for the automotive intelligent cruise control AICC have control in many cases over several antennas, between which they can switch.
According to the invention, these switches are used to operate the Doppler radar system itself or its front end as the Doppler simulator. To this end, the switch is switched over at a frequency that is equivalent to the Doppler frequency shift to be simulated.
The process, according to the invention, can be used, in particular, for measurement purposes to check Doppler radar systems.
In addition, the signal generated by the Doppler simulator can also be used as a transponder in accordance with a transponder process. The transponder works together with an identical system, which serves as the interrogator (interrogator). If the radar signal, transmitted by the interrogator, is received by the transponder, the transponder subjects the signal to the action of a Doppler frequency shift and transmits it back to the interrogator. If there are several transponders, the interrogator recognizes the respective transponder by the size of the frequency shift, generated by the transponder.
The advantage of the process of the present invention lies especially in the fact that a switch-exhibiting Doppler radar system can be switched over from the simulator or transponder mode into the normal radar mode. In addition, the simulator or transponder information can be evaluated analogously to the process used to evaluate normal echo signals.
With this inventive process the radar signal can be modulated on the HF plane so that there is no need for a frequency conversion. As a result, the design of the simulator is simple and inexpensive. In addition, an available radar system front end can be used. In this case it is not absolutely necessary to use the same type of radar system. Thus, for example, the front end of an automobile radar system can be used, in principle, as the Doppler simulator for another Doppler radar system.
In addition, the process of the invention offers, in particular, the following advantages:
The Doppler simulation can be carried out irrespective of frequency fluctuations in the signal, transmitted by the radar system; and
The signal, transmitted by the radar system, is subjected to the action of a Doppler frequency and can be transmitted back again with almost no delay;
The process can be used for pulse modulated and for continuous wave (CW) signal shapes.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.